UK Standard for Heat Interface Units - The BESA

UK Standard for Heat Interface Units

The Building Engineering Services Association (BESA) has published the UK test standard for Heat Interface Units (HIUs).

HIU performance has a major impact on the overall performance of heat networks, both with respect to return temperatures and network sizing.

Up until now many heat networks have failed to achieve their intended efficiency targets, the new standard developed to assess UK heat network operating parameters is regarded as an important step towards improving the overall performance of British district heating schemes.

The standard is based on an initial regime that was developed by engineering and energy consultancy FairHeat as part of a UK government research project into heat network efficiency. Information about this project, including the initial regime and test results from leading HIU manufacturers can be found on their website.

Developed under the auspices of a steering group of industry experts, including: Gareth Jones of Fairheat Ltd, Valeria Khnykina of SSE, Martin Crane of Carbon Alternatives, Neil Shapland of the National House-Building Council, Paul Canning of E.ON Energy, Phil Jones of CIBSE, Rufus Ford of the Department for Business, Energy & Industrial Strategy, Steve Harper of Galliard Homes and Dimitriy Mostovoy of ENGIE, the purpose of the standard is three-fold:

  • To enable the performance of different HIUs to be evaluated within the context of typical UK operating conditions, thereby enabling heat network developers to evaluate the performance of specific HIUs against design requirements.
  • To generate operating data on the expected performance of specific HIUs given “normal” operating parameters, to enable heat network operators to identify anomalous performance.
  • To provide a framework for HIU manufacturers to evaluate the performance of their equipment within the UK context, thereby feeding into their continuous improvement development programmes.

HIUs that are tested according to the test regime specified in the standard will not be ‘certified’. Rather, the intention is to provide test results that will enable performance evaluated within the UK context.

There are two main outputs from this test regime:

  1. Plots of key metrics over the duration of each test; and
  2. Calculation of the annual Volume Weighted Return Temperature (VWART) from the HIU, with this being a composite of estimations of the annual volume-weighted return temperatures for domestic hot water, space heating and keep-warm functions.

In addition, the test regime will evidence compliance with other performance and reliability metrics, such as speed of temperature stabilisation.

UK HIU Test Regime - Technical Specification

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The first manufacturers have now tested against the new standard, the results of which are below

Supplier HIU Serial Number Test Report VWART Calculation Comments

UK Distributor: Frese


Supplier HIU Serial Number Test Report VWART Calculation Comments

Model name:

Manufacturer: Danfoss

Supplier HIU Serial Number Test Report VWART Calculation Comments

Model name: 

Manufacturer: Danfoss

Supplier HIU Serial Number Test Report VWART Calculation Comments

Model Name: DATA

Manufacturer: HSF B.V.

Supplier HIU Serial Number Test Report VWART Calculation Comments

Model name:

MTP4R-1R-TL1/1B (ModuSat XR-ECO TP 55-10R)


Evinox Energy Ltd

If you are a HIU manufacturer, supplier or heat network operator and would like to test a HIU, then please contact Mark Oakes by emailing


The initial technical specification for the HIU standard was produced by FairHeat in partnership with Martin Crane of Carbon Alternatives, under contract to Guru Systems as part of the Heat Networks Demonstration SBRI research project funded by DECC (now BEIS).

As part of the DECC funding, FairHeat commissioned SP Technical Research Institute of Sweden (SP) to modify the “Swedish Test” test rig, utilised for F:103-7e certification, to meet the requirements of the UK test specification. As an output from each test SP produced a test report.

Test Results: Reports and VWART Calculations: DECC funding paid for five of the tests, with the sixth test (Thermal Integration), being paid by the manufacturer.

Further information, including the initial regime ‘Modified Swedish Test UK HIU Test Regime_V1.0’ and the test results for the different HIUs is available from Fairheat’s website.

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